let fs = require("fs");
let read = fs.createReadStream('demo.txt'); //创建可读流￼
let write = fs.createWriteStream('凉州词.txt', { flags: "a" });  //创建可写流￼
read.pipe(write); //将可写流绑定到可读流￼
console.log("已完成")

/**
 * 将write解绑,于是从“凉州词.txt”文件中移除demo.txt
 * 中的内容，最终“凉州词.txt”文件中的内容将不会发生变化。
 */
read.unpipe(write);
console.log("已取消")